As a general method for overcoming error generated in the course of communication, there is such a scheme as automatic repeat request (hereinafter abbreviated ARQ) and error correction. When error is generated in the course of communication, a receiver informs a transmitter of the error generation and the transmitter then retransmits a data block from which the error is generated. This is called ARQ. As representative ARQ schemes, there are stop-and-wait ARQ, continuous ARQ and adaptive ARQ. In order to use ARQ, a reverse channel for feedback is necessary and a buffer is mandatory for ARQ system that should memorize a data block in transmission.
FIG. 1 is a diagram for operational principle of stop-and-wait HARQ.
Referring to FIG. 1, a transmitter Tx transmits a data block corresponding to an index ‘1’. A receiver Rx receives the data block corresponding to the index ‘1’ and then transmits a response signal to the transmitter to inform the transmitter whether the receiver has correctly received the data block. For this, if the receiver decides to have correctly received the data block, it transmits such a response signal as ACK (acknowledgement) to the transmitter. If the receiver decides not to have correctly received the data block, it transmits such a response signal as NAK (No ACK) to the transmitter. If the transmitter Tx receives a NAK signal, it retransmits the data block corresponding to the index ‘1’ to the receiver. In stop-and-wait ARQ scheme, after a data block has been transmitted, it is unable to transmit a next data block until ACK or NAK is received. So, transmission efficiency of the stop-and-wait ARQ scheme is not good. To overcome this disadvantage, continuous ARQ is used. In the continuous ARQ scheme, after data block have been transmitted, if a receiver sends NAK indicating that error has been generated, all block after the error generation are retransmitted or the corresponding erroneous block is retransmitted only. The continuous ARQ is effective if applied to a system having a long radio wave delay. The continuous ARQ (NAK is sent without sending ACK each time error is generated) is classified into two types, Go-Back-NARQ and Selective-Repeat ARQ.
In Go-Back-NARQ, after N continuous data blocks have been transmitted, if the transmission fails, all data blocks transmitted after the erroneous data block are retransmitted. In Selective-Repeat ARQ, an erroneous data block is selectively retransmitted. Theses ARQ schemes are combined with error correction scheme to perform more efficient error control. This is explained as follows.
HARQ (Hybrid Automatic Repeat reQuest) is a technique for controlling error by combining retransmission and error correction with each other and maximizes error correction coding capability of data received in retransmission. The error correction scheme is classified into Backward Error Correction (BEC) and Forward Error Correction (FEC). In BEC, a transmitter retransmits an erroneous data block to restore the erroneous data block. In FEC, a receiver receives an erroneous data block sent by a transmitter and then corrects the corresponding error. Normally, Forward Error Correction (FEC) is frequently used as an error correction scheme in HARQ. If HARQ is adopted, when a receiver fails in restoring a data block, the receiver makes a request for retransmission to a transmitter and then combines stored and retransmitted data together to provide better performance. Stop-and-wait HARQ preferentially used as ARQ scheme is simplest and efficient transmission scheme but has link transmission efficiency lowered due to a rounding trip time (hereinafter abbreviated RTT) taken to exchange ACK/NAK between transmitter and receiver of data. To complement this, N-channel stop-and-wait HARQ protocol scheme is used.
FIG. 2 is a diagram to explain a basic operation of N-channel stop-and-wait HARQ scheme according to a related art.
Referring to FIG. 2, in N-channel stop-and-wait HARQ, a plurality of independent stop-and-wait HARQs are activated for a time not to use a transmission link until ACK/NAK is transmitted and received. Generally, in stop-and-wait HARQ scheme, a data receiver confirms success or failure of data reception through error detection code such as CRC (Cyclic Redundancy Check). In the following description, for clarity and convenience, a data unit for detecting error is named HARQ process block. If data error is not detected, a receiver transmits ACK signal. If error is detected, a receiver transmits NAK signal. Data transmitter having received the ACK signal transmits next data. Data transmitter having received the NAK signal retransmits the corresponding erroneous data. In doing so, a format of the retransmitted data can be changed according to HARQ type. Besides, if transmission band width is large or if data is transmitted via multi-antenna, it is able to transmit a plurality of HARQ process blocks. In particular, a plurality (m) of HARQ processes can simultaneously transmit m HARQ process blocks for a predetermined time or a time interval.
FIG. 3 is a diagram to explain an operation in case of transmitting a plurality of HARQ process blocks via multi-antenna or the like. Referring to FIG. 3, a receiver having received data is able to transmit m ACK/NAK signals for m HARQ process blocks to a data transmitter.
Described in the following description is a resource allocation scheme in a basic physical area of a mobile communication system for transmitting and receiving at least one HARQ process block and at least one corresponding response signal.
FIG. 4 is a diagram for a resource allocating method in time and frequency domains of IEEE 802.16e system as a kind of a multi-carrier system. FIG. 4 shows a frame structure of OFDMA (orthogonal frequency divisional multiple access) physical layer of a related art.
Single frame is constructed with a downlink subframe for downlink, an uplink subframe for uplink and TTG (transmit-receive time gap) and RTG (receive-transmit time gap) as time gaps for discriminating uplink and downlink subframes.
The downlink subframe begins with a preamble used for synchronization and equalization in a physical layer and then defines a whole structure of frame through downlink MAP (DL-MAP) and uplink MAP (UL-MAP) messages in a broadcast format for defining positions and usages of bursts allocated to uplink and downlink, respectively. [In this disclosure, DL-MAP, DL-MAP IE, UL-MAP, UL-MAP IE and the like are implemented with reference to IEEE 802.16Rev-D1 for DL-MAP, DL-MAP IE, UL-MAP, UL-MAP IE and the like of IEEE 802.16e system that supports OFDMA of a related art.]
The DL-MAP message defines a usage assigned per a burst for a downlink interval in a burst-mode physical layer, and the UL-MAP message defines a usage of burst (UL burst) allocated to an uplink interval. In information element configuring DL-MAP, a downlink traffic interval for a user is discriminated by a downlink interval usage code (hereinafter abbreviated DIUC), a connection identifier (CID) and burst position information (subchannel offset, symbol offset, number of subchannels, number of symbols) In information element configuring the UL-MAP message, a usage is decided per CID by uplink interval usage code (hereinafter abbreviated UIUC) and a position of a corresponding interval is specified by duration. In this case, a per-interval usage is decided according to UIUC value used for UL-MAP and each interval starts from a point distant from a previous IE (information element) start point by duration specified by UL-MAP IE.
The UL-MAP assigns usage authority for uplink channel. The UL-MAP defines a usage method for uplink bursts using continuous information elements defining a usage method of each uplink interval and also defines a usage method of OFDMA symbols and uplink resources allocated by a unit of subchannel block. Information element for uplink specifies band allocation information on uplink. Each UL-MAP message contains at least one IE to indicate an end of a last burst. Order of information elements carried by UL-MAP is decided by a physical layer in use.
CID allocates IE as an address of unicast, multicast or broadcast. In case that bandwidth approval is explicitly specified to be assigned, basic CID of user equipment is used as a CID value. UIUC is used to specify an uplink usage format and an uplink burst profile associated with the uplink usage format. In case of each UIUC to be used by UL-MAP, Uplink-Burst-Profile should be included in an uplink channel descriptor (hereinafter abbreviated UCD). Information elements (IEs) should be fully supported by user equipments. In creating UL-MAP message, a base station can use any one of the information elements. TTG (transmit-receive time gap) and RTG (receive-transmit time gap), which are guard times for discriminating uplink and downlink transmission times, are inserted in a middle part and a last part of a frame between uplink and downlink, respectively. For instance, IEEE 802.16e system has RTG=121.2 μS and RTG=40.4 μs.
In the downlink subframe to which downlink burst (DL burst) is allocated, there are PUSC (partial usage of subcarrier) subchannel, diversity subchannel and AMC (adaptive modulation and coding) subchannel. In the uplink subframe, there are diversity subchannel and AMC subchannel. PUSC subchannel, diversity subchannel, AMC subchannel and the like have separate transmission intervals, each of which is constructed with continuous symbols, respectively.
PUSC subchannel in downlink is defined with two symbols and a single PUSC subchannel is constructed with four pilot subcarriers and forty-eight subcarriers. Diversity subchannel in downlink is constructed with forty-eight subcarriers spread on a whole band in a single symbol.
In uplink, a tile configured by collecting three neighbor subcarriers in three continuous symbol intervals is a basic allocation unit to configure a diversity subchannel. The diversity subchannel in uplink is constructed with six tiles each of which is spread on a whole frequency band.
A basic unit for configuring AMC subchannel is a bin constructed with nine neighbor subcarriers in a same symbol. Four bins exist on a single band, and AMC subchannel is constructed with six neighbor bins existing on the same band.
Symbol interval, in which subcarriers exist to configure subchannel, is defined as a slot. Hence, a length of slot varies in accordance with a type of subchannel for dividing uplink and downlink.